Transparent electrically conductive laminate and process for production thereof

ABSTRACT

A transparent conductive laminate comprises a conductive layer. At least one of the following conditions [A] to [C] is satisfied and the ratio of the surface resistance after subjecting the transparent conductive laminate to a 1-hour moist-heat treatment at a temperature of 60° C. and a relative humidity of 90% and then leaving the resultant to stand for 3 minutes at a temperature of 25° C. and a relative humidity of 50% is 0.7 to 1.3 with respect to the surface resistance prior to the treatment: [A] the surface resistance at a white reflectance of 75% is not higher than 1.1×10 3  Ω/□; [B] the surface resistance at a light absorptivity of a carbon nanotube layer of 5% is not higher than 1.1×10 3  Ω/□; and [C] the surface resistance at a total light transmittance of 90% is not higher than 1.1×10 3  Ω/□.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Phase application of PCTInternational Application No. PCT/JP2011/074944, filed Oct. 28, 2011,and claims priority to Japanese Patent Application Nos. 2010-243737,filed Oct. 29, 2010; 2011-074643, filed Mar. 30, 2011; 2011-121497,filed May 31, 2011; 2011-155939, filed Jul. 14, 2011, the disclosures ofeach of which are incorporated herein by reference in their entiretiesfor all purposes.

FIELD OF THE INVENTION

The present invention relates to a transparent conductive laminate. Moreparticularly, the present invention relates to a transparent conductivelaminate having excellent transparent conductivity, heat resistancestability and moist-heat resistance stability; and a production methodthereof. Here, in the present invention, the term “transparentconductive laminate” refers to one in which, on a transparent substrate,at least one layer of a material different from the substrate islaminated by a wet coating method, a dry coating method or the like.

BACKGROUND OF THE INVENTION

Carbon nanotubes have a substantially cylindrical shape obtained bywinding one sheet of graphite. Carbon nanotubes obtained by winding onesheet of graphite in a single layer are referred to as “single-walledcarbon nanotubes” and those which are obtained by winding one sheet ofgraphite in multiple layers are referred to as “multi-walled carbonnanotubes”. Among multi-walled carbon nanotubes, in particular, oneswhich are obtained by winding one sheet of graphite in two layers arereferred to as “double-walled carbon nanotubes”. Carbon nanotubes havethemselves excellent true conductivity and are, therefore, expected tobe used as conductive materials.

In order to prepare a transparent conductive laminate comprising acarbon nanotube, a carbon nanotube is required to be dispersed in adispersion liquid and generally, an ionic dispersant having excellentdispersibility is used therefor.

However, an ionic dispersant is generally an insulative substance andreduces the conductivity of the resulting carbon nanotube transparentconductive laminate. In addition, since an ionic dispersant has an ionicfunctional group, there is a problem that it is easily affected byenvironmental changes such as high temperature and high humidity andthus has poor resistance stability. Therefore, in order to prepare atransparent conductive laminate having high transparent conductivity andexcellent resistance stability, it is believed necessary to remove suchionic dispersant from carbon nanotube layer.

PATENT DOCUMENTS

For example, Patent Document 1 discloses a method of producing aconductive film having high conductivity by coating a film with a carbonnanotube dispersion liquid and then rinsing the resultant with water toremove excess ionic dispersant.

Further, in Patent Document 2, there is disclosed an example where, inorder to stabilize the resistance of a carbon nanotube transparentconductive laminate, an undercoat layer composed of a melamine resin isformed underneath a carbon nanotube layer, thereby improving theresistance stability.

Further, in Patent Document 3, there is disclosed an example where, in atransparent conductive laminate comprising indium tin oxide (ITO) as anelectric conductor, in order to improve the adhesion between a polymersubstrate and an ITO layer which is an inorganic oxide, nitride or oxideof silicon or aluminum is provided as an undercoat layer between thepolymer substrate and the ITO layer.

-   -   Patent Document 1: JP 2009-149516A    -   Patent Document 2: WO2009/107758    -   Patent Document 3: JP 2010-5817A

SUMMARY OF THE INVENTION

In Patent Document 1, there is no disclosure with regard to heatresistance stability and moist-heat resistance stability. In addition,the step of rinsing with water imposes high environmental stress;therefore, it may present a significant hurdle for mass-productionproperty and stabilization of mass production.

In the technology disclosed in Patent Document 2, a melamine resin isemployed as an undercoat layer; however, the heat resistance stabilityis not sufficient.

The ITO constituting the conductive layer is an inorganic substancewhose properties are not impaired in the temperature and humidity rangeswhich a macromolecule, the substrate, can withstand and there is also nodisclosure with regard to heat resistance stability and moist-heatresistance stability.

The present invention was made in view of the above-described problemsand circumstances and provides a transparent conductive laminate havingexcellent heat resistance stability and moist-heat resistance stabilityas well as excellent transparent conductivity.

In order to solve the above-described problems, the transparentconductive laminate according to embodiments of the present inventionhas the following constitution. That is, the transparent conductivelaminate according to embodiments of the present invention is:

a transparent conductive laminate, which comprises a conductive layercontaining a carbon nanotube on a transparent substrate, wherein atleast one of the following conditions [A] to [C] is satisfied and theratio of the surface resistance after subjecting the transparentconductive laminate to a 1-hour moist-heat treatment at a temperature of60° C. and a relative humidity of 90% and then leaving the resultant tostand for 3 minutes at a temperature of 25° C. and a relative humidityof 50% is 0.7 to 1.3 with respect to the surface resistance prior tosaid treatment:

[A] the surface resistance at a white reflectance of 75% is 1.1×10³ Ω/□or less;

[B] the surface resistance at a light absorptivity of a carbon nanotubelayer of 5% is 1.1×10³ Ω/□ or less; and

[C] the surface resistance at a total light transmittance of 90% is1.1×10³ Ω/□ or less.

Further, the method of producing a transparent conductive laminateaccording to embodiments of the present invention has the followingconstitution. That is, the method of producing a transparent conductivelaminate according to embodiments of the present invention is:

a method of producing a transparent conductive laminate, which comprisesthe steps of: forming an undercoat layer on a transparent substrate,wherein a water contact angle of said undercoat layer is of 5 to 25°;coating a carbon nanotube dispersion liquid containing a dispersant onthe undercoat layer; and drying the resultant to remove a dispersionmedium from the above-described carbon nanotube dispersion liquid coatedon the undercoat layer.

The electric paper according to embodiments of the present invention hasthe following constitution. That is, the electric paper according toembodiments of the present invention is:

an electric paper comprising the above-described transparent conductivelaminate.

The touch screen according to embodiments of the present invention hasthe following constitution. That is, the touch screen according toembodiments of the present invention is:

a touch screen comprising the above-described transparent conductivelaminate.

In the transparent conductive laminate according to the presentinvention, it is preferred that the ratio of the surface resistanceafter subjecting the transparent conductive laminate to a 1-hour heattreatment at a temperature of 150° C. and then leaving the resultant tostand for 24 hours at a temperature of 25° C. and a relative humidity of50% be 0.7 to 1.3 with respect to the surface resistance prior to thetreatment.

In the transparent conductive laminate according to the presentinvention, it is preferred that the ratio of the surface resistanceafter subjecting the transparent conductive laminate to a 500-hour heattreatment at a temperature of 80° C. and then leaving the resultant tostand for 3 minutes at a temperature of 25° C. and a relative humidityof 50% be 0.7 to 1.3 with respect to the surface resistance prior to thetreatment.

In the transparent conductive laminate according to the presentinvention, it is preferred that an undercoat layer containing aninorganic oxide be arranged underneath the above-described conductivelayer.

In the transparent conductive laminate according to the presentinvention, it is preferred that the above-described inorganic oxidecontain alumina and/or silica as a main component(s).

In the transparent conductive laminate according to the presentinvention, it is preferred that the above-described undercoat layercontain a complex of a silica microparticle and a polysilicate as a maincomponent.

In the transparent conductive laminate according to the presentinvention, it is preferred that the above-described silica microparticlehave a diameter in the range of 10 nm to 200 nm.

In the method of producing a transparent conductive laminate accordingto the present invention, it is preferred that the above-describedcarbon nanotube dispersion liquid have a pH in the range of 5.5 to 11.

In the method of producing a transparent conductive laminate accordingto the present invention, it is preferred that, in the above-describedcoating step and/or drying step, the dispersant be transferred from thecarbon nanotube surface and/or the carbon nanotube dispersion liquid tothe above-described undercoat layer.

In the method of producing a transparent conductive laminate accordingto the present invention, it is preferred that the mass ratio of thedispersant be 0.5 to 9 with respect to the carbon nanotube contained inthe above-described carbon nanotube dispersion liquid.

According to the present invention, since a carbon nanotube can becoated on a transparent substrate in a highly dispersed conditionwithout being aggregated, a transparent conductive laminate having hightransparent conductivity can be obtained. Also, since a dispersant,which is an insulative material, is transferred from a carbon nanotubelayer onto an undercoat layer, a transparent conductive laminate havingexcellent transparent conductivity, heat resistance stability andmoist-heat resistance stability can be obtained.

That is, high initial transparent conductivity as well as heatresistance and moist-heat resistance stabilities, which areconventionally not easily attained at the same time, can be realized bya process imposing low environmental stress.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing which illustrates a corona treatment method whichmay be used in the present invention.

FIG. 2 is a drawing which illustrates a method of measuring the whitereflectance.

FIG. 3 is one example of an image showing the surface of an undercoatlayer in the present invention, which was taken under an atomic forcemicroscope (hereinafter, referred to as “AFM”).

FIG. 4 is a drawing which illustrates an alumina vapor deposition methodthat can be used in the present invention.

FIG. 5 is a schematic diagram showing a chemical vapor depositionapparatus that can be used in the present invention.

FIG. 6 is a drawing which illustrates the results of photoelectronspectrometry in an example of the present invention.

FIG. 7 a reference drawing of the results of photoelectron spectrometry,showing the structural formula of carboxymethylcellulose.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The method of producing a transparent conductive laminate according toembodiments of the present invention comprises the steps of: forming anundercoat layer on a transparent substrate, which undercoat layer has awater contact angle of 5 to 25′; coating a carbon nanotube dispersionliquid containing a dispersant (hereinafter, may be simply referred toas “dispersion liquid”) on the undercoat layer; and drying the resultantto remove a dispersion medium from the above-described carbon nanotubedispersion liquid containing a dispersant.

In the step of forming an undercoat layer, dry coating or wet coatingcan be adopted. It is preferred that the resulting undercoat layer havea thickness of 1 to 500 nm.

In the coating step, in order to form a carbon nanotube layer on theundercoat layer, a carbon nanotube dispersion liquid containing adispersant is provided by wet coating. The carbon nanotube dispersionliquid used here is a mixture of a carbon nanotube, a dispersant and adispersion medium, which is water, and it is preferred that thedispersant be contained at a mass ratio of 0.5 to 9 with respect to thecarbon nanotube. It is preferred that this dispersion liquid be coatedon the undercoat layer such that the amount of the carbon nanotube afterdrying becomes 1 to 40 mg/m².

Examples of the step of drying to remove a dispersion medium from thecoated carbon nanotube dispersion liquid, which is performed after thecoating step, include convective hot-air drying in which hot air isblown to a substrate; radiation electrothermal drying in which asubstrate is allowed to absorb infrared radiation irradiated from aninfrared dryer and the thus absorbed infrared radiation is converted toheat so as to dry the substrate by the heat; and conductiveelectrothermal drying in which drying is performed by thermal conductionfrom a wall surface heated by a heating medium. Thereamong, convectivehot-air drying is preferred since the drying rate is high.

Further, in the present invention, it is preferred that the dispersantbe transferred to the above-described undercoat layer in theabove-described coating step and/or drying step.

Generally, in a carbon nanotube dispersion liquid, due to highπ-electron interaction working between the side walls of carbonnanotubes, the carbon nanotubes are likely to aggregate into a bundlestate. By applying a dispersion liquid in which this bundle state isresolved and carbon nanotubes are separated from one another anddispersed, the conductivity of the resulting carbon nanotube layer isexpected to be improved. Further, the longer the carbon nanotubes, themore the number of contact points among the carbon nanotubes isincreased, so that the conductivity of the resulting carbon nanotubelayer is improved. However, in a transparent conductive laminateprepared by coating and then drying a carbon nanotube dispersion liquidon a transparent substrate, while an increased amount of dispersant inthe dispersion liquid contributes to an improvement in the conductivityby resolving the above-described bundle state and preventing carbonnanotubes from breaking at the time of their dispersion, there is aproblem that these effects are cancelled as the use of such dispersionliquid leads to an increase in the ratio of the dispersant, aninsulative material, in the resulting carbon layer, adversely affectingthe conductivity. Furthermore, an increase in the amount of dispersantcontained in the carbon nanotube layer also has a problem in that theresistance stability of the resulting transparent conductive laminate isdeteriorated when it is heat-treated or placed in a high-temperature andhigh-humidity condition. In a preferred mode of the present invention,the amount of dispersant in the dispersion liquid is increased to havecarbon nanotubes in a highly dispersed state and inhibit their breakageand, in the step of coating and/or drying the carbon nanotube dispersionliquid on a hydrophilic undercoat layer, the dispersant is transferredto the undercoat layer, thereby the amount of the dispersant in theresulting carbon nanotube layer can be reduced and a transparentconductive laminate having superior transparent conductivity andresistance stability as compared to before can be obtained.

[Transparent Substrate]

Examples of the material of the transparent substrate used in thepresent invention include resins and glasses. As the resin, for example,a polyester such as polyethylene terephthalate (PET) or polyethylenenaphthalate (PEN), a polycarbonate (PC), a polymethyl methacrylate(PMMA), a polyimide, a polyphenylene sulfide, an aramids, apolypropylene, a polyethylene, a polylactic acid, a polyvinyl chloride,a polymethyl methacrylate, an alicyclic acrylic resin, a cycloolefinresin or a triacetylcellulose may be employed. As the glass, an ordinarysoda glass may be employed. Further, a plurality of these transparentsubstrates may be used in combination as well. For example, thetransparent substrate may be one which is composed of a combination of aresin and a glass or a complex transparent substrate such as oneobtained by laminating two or more resins. The transparent substrate mayalso be one in which a hardcoat is arranged on a resin film. The type ofthe transparent substrate is not restricted to those described in theabove and the most appropriate one can be selected in accordance withthe intended use as well as from the standpoints of the durability, costand the like. The thickness of the transparent substrate is notparticularly restricted; however, in cases where it is used in anelectrode related to a display such as a touch screen, a liquid crystaldisplay, an organic electroluminescence or an electric paper, thethickness of the transparent substrate is preferably in the range of 10μm to 1,000 μm.

[Undercoat Layer]

In the present invention, an undercoat layer is preferably provided onthe above-described transparent substrate. It is preferred that thematerial of the undercoat layer be one having high hydrophilicity.Specifically, a material having a water contact angle in the range of 5to 25° is preferred. More specifically, an inorganic oxide is preferablyemployed. More preferably, the material is titania, alumina or silica.These substances are preferred because they have a hydrophilic group-OHgroup on the surface and high hydrophilicity can be thus attained.Further, it is more preferred that the undercoat layer contain a complexof a silica microparticle and a polysilicate as a main component.

Further, it is more preferred that irregularities be formed on thesurface of the undercoat layer. By forming irregularities, in thecoating step and/or the drying step, the area of the undercoat layer towhich the dispersant can be transferred is increased and the amount ofthe dispersant transferred can be thus increased. As a result, thetransparent conductivity and the resistance stability of the transparentconductive laminate can be further improved. In order to easily formirregularities of a desired range, it is preferred that the inorganicoxide microparticles to be contained in the undercoat layer have adiameter in the range of 10 to 200 nm.

In addition, in order to further hydrophilize the undercoat layer, theabove-described hydrophilic functional group may be expressed byperforming a surface hydrophilization treatment. Examples ofhydrophilization method include physical treatments such as coronatreatment, plasma treatment and flame treatment; and chemical treatmentssuch as acid treatment and alkali treatment. Thereamong, coronatreatment and plasma treatment are preferred. A corona treatment can beperformed by using, for example, such an apparatus shown in FIG. 1. Suchcorona treatment can be performed as follows. Using a high-voltageapplication device 101, a DC voltage of 10 to 100 kV is generatedbetween ground (not shown) and an electrode 102. Then, after separatingthe electrode 102 and a transparent substrate 104 by a distance of 50 to200 μm, a partition wall 102 is arranged therebetween and the electrodeis moved at a speed of 1 to 10 cm/sec in the direction of the arrowindicated as “A” in FIG. 1. By performing these operations, surfaceproperties including a water contact angle in the above-described rangecan be attained.

[Method of Forming Undercoat Layer]

In the present invention, the method of forming an undercoat layer on atransparent substrate is not particularly restricted. A known wetcoating method, for example, spray coating, immersion coating, spincoating, knife coating, kiss coating, gravure coating, slot-die coating,roll coating, bar coating, screen printing, ink jet printing, padprinting or other type of printing method may be employed. Further, adry coating method may be employed as well. As the dry coating method,for example, physical vapor growth, such as sputtering or vapordeposition, or chemical vapor deposition can be utilized. Further, thecoating may be performed in plural times and two different coatingmethods may also be used in combination. As the coating method, gravurecoating and bar coating, which are wet coating, are preferred.

[Adjustment of Undercoat Layer Thickness]

The thickness of the undercoat layer is not restricted as long as thedispersant can be transferred thereto at the time of coating the carbonnanotube dispersion liquid. Any thickness at which an anti-reflectioneffect by optical interference can be effectively attained is preferredsince such a thickness allows an improvement in the light transmittance.Accordingly, it is preferred that the thickness of the undercoat layerbe, combined with that of the later-described overcoat layer, in therange of 80 to 120 nm.

[Water Contact Angle of Undercoat Layer]

The water contact angle can be measured using a commercially availablecontact angle measuring apparatus. In the measurement of the watercontact angle, in accordance with JIS R 3257 (1999), in an atmospherehaving a room temperature of 25° C. and a relative humidity of 50%, 1 to4 μL of water is dropped onto the undercoat layer surface using asyringe and a droplet is observed from a horizontal cross-section todetermine the angle created between a tangent line of the droplet edgeand the film plane.

[Carbon Nanotube]

The carbon nanotube used in the present invention is not particularlyrestricted as long as it is one having a substantially cylindrical shapeobtained by winding one sheet of graphite. Either of a single-walledcarbon nanotube obtained by winding one sheet of graphite in singlelayer and a multi-walled carbon nanotube obtained by winding one sheetof graphite in multiple layers may be employed; however, preferredthereamong is particularly a carbon nanotube in which at least 50 out of100 carbon nanotubes are double-walled carbon nanotubes obtained bywinding one sheet of graphite in two layers since a such carbon nanotubehas extremely high conductivity as well as extremely high dispersibilityin a coating dispersion liquid. It is more preferred that at least 75out of 100 carbon nanotubes be double-walled carbon nanotubes and it ismost preferred that at least 80 out of 100 carbon nanotubes bedouble-walled carbon nanotubes. It is noted here that the conditionwhere 50 out of 100 carbon nanotubes are double-walled carbon nanotubesmay be indicated as “the ratio of double-walled carbon nanotube is 50%”.

Furthermore, a double-walled carbon nanotube is preferred also from thepoint that the intrinsic functions such as conductivity are not impairedeven when the surface thereof is functionalized by an acid treatment orthe like.

The carbon nanotube is produced by, for example, the followingprocedures. In a vertical reactor, a powder-form catalyst in which ironis supported on magnesia is provided on the entire surface of thereactor in the direction of horizontal cross-section of the reactor.Methane is then supplied to the reactor in the vertical direction so asto bring the thus supplied methane into contact with the above-describedcatalyst at a temperature of 500 to 1,200° C. After producing a carbonnanotube, the thus obtained carbon nanotube may be subjected to anoxidation treatment to obtain a carbon nanotube containing single-walledto 5-walled carbon nanotubes. After this production, the thus obtainedcarbon nanotube may be subjected to an oxidation treatment, thereby theratio of the single-walled to 5-layered carbon nanotubes, particularlythe ratio of the double-walled to 5-walled nanotubes, can be increased.This oxidation treatment is performed by using, for example, a nitricacid treatment method. Nitric acid is preferred since it acts as adopant for carbon nanotubes. A dopant provides a carbon nanotube withexcess electrons or functions to deprive electrons to form a hole. Adopant improves the conductivity of a carbon nanotube by generating acarrier capable of moving freely. The nitric acid treatment method isnot particularly restricted as long as the carbon nanotube according tothe present invention can be obtained; however, it is usually performedin an oil bath at 140° C. The duration of the nitric acid treatment isalso not particularly restricted; however, it is preferably in the rangeof 5 hours to 50 hours.

[Dispersant]

As the dispersant of the carbon nanotube, for example, surfactants andvariety of polymer materials (water-soluble polymer materials) may beemployed; however, an ionic polymer material having high dispersibilityis preferred. Examples of the ionic polymer material include anionicpolymer materials, cationic polymer materials and amphoteric polymermaterials. Any type of such ionic polymer material may be used as longas it has high carbon nanotube-dispersing capacity and is capable ofretaining dispersion; however, anionic polymer materials are preferredsince they have excellent dispersibility and dispersion-retainingproperty. Thereamong, carboxymethylcellulose and salts thereof (such assodium salt and ammonium salt) and polystyrene sulfonic acid salts arepreferred since they are capable of efficiently dispersing the carbonnanotube in a carbon nanotube dispersion liquid.

In the present invention, in cases where a carboxymethylcellulose saltor a polystyrene sulfonic acid salt is used, as the cationic substanceconstituting the salt, for example, a cation of an alkali metal such aslithium, sodium or potassium; a cation of an alkaline earth metal suchas calcium, magnesium or barium; an ammonium ion; an onium ion of anorganic amine such as monoethanolamine, diethanolamine, triethanolamine,morpholine, ethylamine, butylamine, coconut oil amine, tallow amine,ethylenediamine, hexamethylenediamine, diethylenetriamine orpolyethyleneimine; or a polyethylene oxide adduct thereof can be used;however, the cationic substance constituting the salt is not restrictedto these.

[Dispersion Medium]

As the dispersion medium used in the present invention, from theviewpoints that, for example, the above-described dispersant can besafely dissolved and the resulting waste liquid is easily treated, wateris preferred.

[Carbon Nanotube Dispersion Liquid]

The method of preparing the carbon nanotube dispersion liquid used inthe present invention is not particularly restricted and the preparationcan be performed by, for example, the following procedures.

Since the treatment time at the time of dispersion can be shortened, itis preferred to once prepare a dispersion liquid which contains thecarbon nanotube in the concentration range of 0.003 to 0.15% by mass inthe dispersion medium and then dilute the resultant to a prescribedconcentration. In the present invention, the mass ratio of thedispersant is preferably not higher than 10 with respect to the carbonnanotube. In such preferred range, uniform dispersion is easily attainedand there is no effect of impairing the conductivity. The mass ratio ismore preferably 0.5 to 9, still more preferably 1 to 6. A mass ratio of2 to 3 is particularly preferred since high transparent conductivity canbe attained. Examples of a dispersion means used in the preparation ofthe dispersion liquid include mixing a carbon nanotube and a dispersantin a dispersion medium using a mixing/dispersion apparatus which iscommonly used in the production of a coating (for example, a ball mill,a beads mill, a sand mill, a roll mill, a homogenizer, an ultrasonichomogenizer, a high-pressure homogenizer, an ultrasonic apparatus, anattritor, a desorber or a paint shaker). Further, dispersion may also becarried out stepwise by using a plurality of these mixing/dispersionapparatuses in combination. Thereamong, a method in which dispersion iscarried out using an ultrasonic apparatus after performing preliminarydispersion using a vibration ball mil is preferred since thedispersibility of the carbon nanotube in the resulting dispersion liquidused for coating is favorable.

[Characteristics of Carbon Nanotube Dispersion Liquid]

It is preferred that the dispersion liquid used in the present inventionhave a pH in the range of 5.5 to 11.

When the pH of the carbon nanotube dispersion liquid is in the range of5.5 to 11, the ionization degrees of acidic functional groups of forexample, carboxylic acid modifying the carbon nanotube surface andcarboxylic acid contained in the dispersant surrounding the carbonnanotube are improved, so that the carbon nanotube or the dispersanttherearound becomes negatively charged. In this manner, by allowingmutual electrostatic repulsion of the carbon nanotube or the dispersanttherearound to occur, the dispersibility of the carbon nanotube can befurther improved and the bundle diameter thereof can be made small. ThepH is adjusted preferably in the step of mixing and dispersing thedispersant using the above-described mixing/dispersion apparatus;however, the same effects can also be attained by performing theadjustment after the dispersion step.

The pH of the carbon nanotube dispersion liquid can be adjusted byadding thereto an acidic substance or a basic substance in accordancewith the Arrhenius Law. Examples of the acidic substance include, asprotonic acids, inorganic acids such as hydrochloric acid, sulfuricacid, nitric acid, phosphoric acid, fluoroboric acid, hydrofluoric acidand perchloric acid; organic carboxylic acids; phenols; and organicsulfonic acids. Further, examples of the organic carboxylic acidsinclude formic acid, acetic acid, nitric acid, benzoic acid, phthalicacid, maleic acid, fumaric acid, malonic acid, tartaric acid, citricacid, lactic acid, succinic acid, monochloroacetic acid, dichloroaceticacid, trichloroacetic acid, trifluoroacetic acid, nitroacetic acid andtriphenylacetic acid. Examples of the organic sulfonic acids includealkylbenzenesulfonic acid, alkylnaphthalenesulfonic acid,alkylnaphthalenedisulfonic acid, naphthalenesulfonic acid-formalinpolycondensate, melamine sulfonic acid-formalin polycondensate,naphthalenedisulfonic acid, naphthalenetrisulfonic acid,dinaphthylmethanedisulfonic acid, anthraquinonesulfonic acid,anthraquinonedisulfonic acid, anthracenesulfonic acid and pyrenesulfonicacid. Among these acidic substances, volatile acids that are vaporizedat the time of coating and drying the dispersion liquid, such ashydrochloric acid and nitric acid, are preferred.

Examples of the basic substance include sodium hydroxide, potassiumhydroxide, calcium hydroxide and ammonia. Thereamong, volatile basesthat are vaporized at the time of coating and drying the dispersionliquid, such as ammonia, are preferred.

[pH Adjustment of Carbon Nanotube Dispersion Liquid]

The pH of the carbon nanotube dispersion liquid is adjusted by addingthe above-described acidic substance and/or basic substance until adesired pH is attained while measuring the pH. Examples of the method ofmeasuring the pH include a method in which a pH test paper such aslitmus paper is used, a hydrogen electrode method, a quinhydroneelectrode method, an antimony electrode method and a glass electrodemethod. Thereamong, a glass electrode method is preferred since it issimple and capable of providing the required accuracy. Further, in casewhere an acidic substance or a basic substance was added excessively andthe pH became higher than a desired value, the pH can be adjusted byadding a substance having the opposite property. As the acidic substanceand the basic substance to be used in such adjustment, nitric acid andammonia are preferred, respectively.

[Formation of Carbon Nanotube Layer]

In the method of producing a transparent conductive laminate accordingto an embodiment of the present invention, a carbon nanotube layer isformed through the step of coating a carbon nanotube dispersion liquidon a transparent substrate and the subsequent step of drying theresultant to remove a dispersion medium. In the coating step, it isbelieved that, when a dispersion liquid obtained by the above-describedmethod is coated on a transparent substrate having the above-describedundercoat layer formed thereon, a dispersant having a hydrophilic moietyis drawn to the surface of the undercoat layer having a hydrophilicgroup, so that the dispersant is adsorbed to the surface of theundercoat layer. Subsequently, a carbon nanotube layer is formed bydrying the dispersion medium and fixing the carbon nanotube onto theundercoat layer. Here, it is believed that, due to the dispersion mediumremaining on the undercoat layer, as long as the dispersant is in acondition where it is capable of moving from the carbon nanotube to thesurface of the undercoat layer, the dispersant is drawn and adsorbed tothe surface of the undercoat layer having a hydrophilic group in thesame manner as in the coating step. In this manner, it is believed thatthe amount of the dispersant in the carbon nanotube layer is reduced bythe adsorption of the dispersant to the undercoat layer having ahydrophilic group. Such adsorption of the dispersant to the undercoatlayer is attained by using a hydrophilic undercoat layer having a watercontact angle of 5° to 25°. Further, it is preferred that the carbonnanotube dispersion liquid be coated at a coating thickness in the rangeof 1 μm to 50 μm and that the time for the dispersion medium to beremoved from the carbon nanotube layer by drying be in the range of 0.1second to 100 seconds since the adsorption of the dispersant by suchmechanism can be more effectively generated.

An example of the method for verifying this phenomenon is X-rayphotoelectron spectrometry (XPS). In XPS, a substance is irradiated withX-ray to excite an electron in the atomic orbital and allow them to bereleased from the system as a photoelectron and the energy value thereofis measured.

This photoelectron energy value is represented by the following formula.

E=hν−E _(B)

(E: photoelectron energy value, hv: energy value of irradiated X-ray,E_(B): electron binding energy)

The E_(B) can be determined by irradiating X-ray having a certain energyvalue and measuring the energy value of the released photoelectron.Since the E_(B) is an orbital energy peculiar to each element, the typeof the element can be identified from this value. Further, even in thesame element, the peak of the energy value shifts depending on itsbinding condition. Thus, by measuring this shift, the binding conditioncan also be determined.

In the present invention, the amount of the dispersant is determinedsemiquantitatively from peaks that are peculiar to the dispersant. Forexample, in carboxymethylcellulose, carbon atoms having a bindingcondition of —COO, —COO— or —CO— are present. By measuring these peaksand performing appropriate data processing, the amounts of dispersantscan be compared. Further, the detection depth of XPS is dependent on themean free path of the substance as well; however, by adjusting thephotoelectron escape angle (tilt of the detector with respect to thesample surface), the detection depth can be controlled to roughlyseveral nanometers or so. This value is almost the same as the estimatedthickness of the carbon nanotube layer according to the presentinvention and can thus provide information on the carbon nanotube layer.

By determining the E_(B) of the carbon atoms in the outermost surface ofthe carbon nanotube layer by XPS, it was able to verify that the amountof the dispersant in the carbon nanotube layer is smaller when anundercoat layer is present as compared to when no undercoat layer ispresent, so that it was supported that the dispersant transferred to theundercoat layer.

In the present invention, the method of coating the dispersion liquid onthe transparent substrate is not particularly restricted. A knowncoating method, for example, spray coating, immersion coating, spincoating, knife coating, kiss coating, gravure coating, slot-die coating,bar coating, roll coating, screen printing, ink jet printing, padprinting or other type of printing method may be employed. Further, thecoating may be performed in plural times and two different coatingmethods may be used in combination as well. Gravure coating and barcoating are the most preferred coating methods.

[Thickness Adjustment of Carbon Nanotube Layer]

The coating thickness at which the carbon nanotube dispersion liquid iscoated on the transparent substrate (thickness in wet condition) is alsodependent on the concentration of the carbon nanotube dispersion liquid;therefore, the coating thickness can be adjusted as appropriate so thata desired surface resistance can be attained. In the present invention,the amount of carbon nanotube to be coated can be easily adjusted so asto achieve a variety of applications where conductivity is required. Forexample, as long as the coating amount is 1 m g/m² to 40 mg/m², thesurface resistance can be attained at 1×10° to 1×10⁴ ∩/□, which ispreferred.

[Overcoat Layer]

In the present invention, after the formation of the carbon nanotubelayer, an overcoat layer composed of a transparent coating film may beformed on the carbon nanotube layer. It is preferred that an overcoatlayer be formed since the transparent conductivity, heat resistancestability and moist-heat resistance stability can be thereby furtherimproved.

As the material of the overcoat layer, either of an organic material andan inorganic material can be used; however, from the standpoint of theresistance stability, an inorganic material is preferred. Examples ofthe inorganic material include metal oxides such as silica, tin oxide,alumina, zirconia and titania, and from the standpoint of the resistancestability, silica is preferred.

[Method of Forming Overcoat Layer]

In the present invention, the method of forming an overcoat on a carbonnanotube layer is not particularly restricted. A known wet coatingmethod, for example, spray coating, immersion coating, spin coating,knife coating, kiss coating, roll coating, gravure coating, slot-diecoating, bar coating, screen printing, ink jet printing, pad printing orother type of printing method may be employed. Further, a dry coatingmethod may be employed as well. As the dry coating method, for example,physical vapor growth, such as sputtering or vapor deposition, orchemical vapor deposition can be utilized. Further, the operation ofproviding an overcoat layer on a carbon nanotube layer may be performedin plural times and two different coating methods may also be used incombination. Gravure coating and bar coating, which are wet coating, arepreferred methods.

In the method of forming a silica layer using wet coating, it ispreferred to use an organic silane compound, and examples of such methodinclude a method in which the above-described wet coating is performedusing, as a coating solution, a solution which is prepared by dissolvinga silica sol produced by hydrolyzation of an organic silane compoundsuch as tetraalkoxysilane (e.g. tetramethoxysilane, tetraethoxysilane,tetra-n-propoxysilane, tetra-iso-propoxysilane or tetra-n-butoxysilane)in a solvent and at the time of drying the solvent, silanol groups areallowed to undergo dehydration condensation with each other to form asilica thin film.

The thickness of the overcoat layer is controlled by adjusting theconcentration of the silica sol in the coating solution and the coatingthickness at the time of coating. Any thickness at which ananti-reflection effect by optical interference can be effectivelyattained is preferred since such a thickness allows an improvement inthe light transmittance. Accordingly, as described in the above, it ispreferred that the thickness of the overcoat layer be, combined withthat of the undercoat layer, in the range of 80 to 120 nm. Further, byincreasing the thickness of the overcoat layer, scattering of a dopantimproving the conductivity of the carbon nanotube, such as nitric acid,can be prevented and long-term heat resistance can be improved. Thethickness of the overcoat layer effective in preventing this scatteringof a dopant is not less than 40 nm. Further, considering the range ofthe total thickness of the undercoat layer and the overcoat layer forattaining the above-described anti-reflection effect, it is morepreferred that the thickness of the overcoat layer be not less than 40nm and not greater than 120 nm.

[Transparent Conductivity]

A transparent conductive laminate having excellent transparentconductivity can be obtained in the above-described manner. The term“transparent conductivity” means that transparency and conductivity areattained at the same time.

A representative index of the transparency is total light transmittanceand examples of similar index include white reflectance and lightabsorptivity of the carbon nanotube layer (the white reflectance andlight absorptivity of the carbon nanotube layer will be describedlayer). The total light transmittance is in the range of preferably 80%to 93%, more preferably 90% to 93%.

In the present invention, as an index of the transparency, in additionto the total light transmittance, the white reflectance or the lightabsorptivity of the carbon nanotube layer may also be used. The “whitereflectance” in the present invention (hereinafter, indicated as “thewhite reflectance”) represents a ratio of the reflected light to theincoming light when a white reflection plate 201, an adhesive layer 202and a transparent conductive laminate 203 are laminated as shown in FIG.2 and a light having a wavelength of 550 nm is irradiated from the sideof the transparent conductive laminate. As long as the thickness of thisadhesive layer and the refractive index are in the range of 20 μm to 40μm and 1.4 to 1.6, respectively, the transparent conductive laminate issuitable for the measurement of the white reflectance prescribed in thepresent invention. The material of the adhesive is not particularlyrestricted as long as the thickness of the adhesive layer and thereflective index are in the above-described respective ranges. Forexample, materials such as acryls, urethanes, olefins, celluoses,ethylene-vinyl acetates, epoxy-based materials, vinyl chlorides,chloroprene rubbers, vinyl acetates, cyanoacrylates, silicones, phenolresins, polyimides, polystyrenes and melamines may be employed asappropriate.

In the present invention, examples of other index that can be used asthe index of transparency include the light absorptivity of the carbonnanotube layer. The light absorptivity of the carbon nanotube layer at awavelength of 500 nm is an index represented by the following formula.

Light absorptivity of carbon nanotube layer (%)=100%−Light transmittance(%)−Light reflectance of conductive surface (%)−Light reflectance ofsurface opposite to conductive surface (%)

As an index of conductivity, the surface resistance is used. The lowerthe surface resistance, the higher the conductivity. The surfaceresistance is in the range of preferably 1×10° to 1×10⁴ Ω/□, morepreferably 1×10° to 1×10³ Ω/□.

The conductivity (surface resistance) and the transparency (such astotal light transmittance) can be adjusted by changing the coatingamount of the carbon nanotube. However, when the coating amount of thecarbon nanotube is small, the transparency is high while theconductivity is low, and when the coating amount is large, thetransparency is low while the conductivity is high. That is, theconductivity and the transparency are in a trade-off relationship;therefore, it is difficult to satisfy both of these properties at thesame time. Because of such relationship, in order to compare thetransparent conductivity, it is required that either of these indices befixed and the other index be compared. In the present invention, whencomparing the transparent conductivity, the surface resistance under acertain transparency is used as an index.

That is, in cases where the total light transmittance is selected as anindex of the transparency, the surface resistance at a total lighttransmittance of 90% is used as the index. In the transparent conductivelaminate according to the present invention, the surface resistance at atotal light transmittance of 90% is preferably not higher than 1.1×10³Ω/□.

In the present invention, in cases where the white reflectance isselected as an index of the transparency, the surface resistance at awhite reflectance of 75% is used as the index. In the transparentconductive laminate obtained by the present invention, the surfaceresistance at a white reflectance of 75% is preferably not higher than1.1×10³ Ω/□.

In the present invention, in cases where the light absorptivity of thecarbon nanotube layer is selected as an index of the transparency, thesurface resistance at a light absorptivity of the carbon nanotube layerof 5% is used as the index. In the transparent electrically-conductivitylaminate obtained by the present invention, the surface resistance at alight absorptivity of the carbon nanotube layer of 5% is preferably nothigher than 1.1×10³ Ω/□.

As the above-described index of the transparency, the total lighttransmittance of a laminate comprising an overcoat layer, a carbonnanotube layer, an undercoat layer and a transparent substrate ispractically meaningful. Accordingly, the index can be used when arelative comparison is performed with a laminate of a certain overcoatlayer and undercoat layer. However, since the light reflectance of theconductive surface as well as the total light transmittance varydepending on the refractive indices of the overcoat layer and undercoatlayer, in cases where carbon nanotube layers alone are compared, it ispreferred to use the white reflectance or the light absorptivity thereofas an index.

[Moist-heat Resistance Stability]

By the method of producing a transparent conductive laminate accordingto the present invention, a transparent conductive laminate whichsatisfies the above-described conductivity and has excellent moist-heatresistance stability can be obtained. In the present invention, as anindex of the moist-heat resistance stability, the ratio of the surfaceresistance after subjecting the transparent conductive laminate to a1-hour moist-heat treatment at a temperature of 60° C. and a relativehumidity of 90% and then leaving the resultant to stand for 3 minutes ata temperature of 25° C. and a relative humidity of 50% with respect tothe surface resistance prior to the treatment is employed. In thetransparent conductive laminate according to an embodiment of thepresent invention, this moist-heat resistance stability is 0.7 to 1.3,preferably 0.8 to 1.2.

[Heat Resistance Stability]

By a preferred method of producing a transparent conductive laminateaccording to the present invention, a transparent conductive laminatewhich also has excellent heat resistance stability can be obtained. Inthe present invention, as an index of the heat resistance stability, theratio of the surface resistance after subjecting the transparentconductive laminate to a 1-hour heat treatment at a temperature of 150°C. and then leaving the resultant to stand for 24 hours at a temperatureof 25° C. and a relative humidity of 50% with respect to the surfaceresistance prior to the treatment is employed. Here, the relativelyhumidity is not controlled in the heat treatment at 150° C.; however,since the saturated water vapor pressure at 150° C. is 4.8 atm and thatat 25° C., which is normal temperature, is 0.03 atom, even if therelative humidity varied at normal temperature, when the temperature isincreased to 150° C., the relative humidity can be regarded to besubstantially 0. In transparent conductive laminate according to thepresent invention, the heat resistance stability is preferably 0.7 to1.3, more preferably 0.8 to 1.2.

[Long-term Heat Resistance Stability]

By a more preferred method of producing a transparent conductivelaminate according to the present invention, a transparent conductivelaminate which also has excellent long-term heat resistance stabilitycan be obtained. In the present invention, as an index of the long-termheat resistance stability, the ratio of the surface resistance aftersubjecting the transparent conductive laminate to a 500-hour heattreatment at a temperature of 80° C. and then leaving the resultant tostand for 3 minutes at a temperature of 25° C. and a relative humidityof 50% with respect to the surface resistance prior to the treatment isemployed. Here, the relatively humidity is not controlled in the heattreatment at 80° C.; however, since the saturated water vapor pressureat 80° C. is 0.47 atm and that at 25° C., which is normal temperature,is 0.03 atom, even if the relative humidity varied at normaltemperature, when the temperature is increased to 150° C., the relativehumidity can be regarded to be substantially 0. In transparentconductive laminate according to the present invention, the long-termheat resistance stability is preferably 0.7 to 1.3, more preferably 0.8to 1.2.

EXAMPLES

The present invention will now be described in more detail by way ofexamples thereof; however, the present invention is not restrictedthereto. The measurement methods used in the examples are describedbelow. Unless otherwise specified, the number of measurements, n, was 2and an average thereof was used.

(1) Surface Resistance

A transparent conductive laminate was sampled in a size of 5 cm×10 cmand a probe was brought into close contact with the central part of thecarbon nanotube layer side of the thus sampled transparent conductivelaminate to measure the resistance by a four-probe method at roomtemperature. A resistivity meter, model MCP-T360 manufactured by DIAInstruments Co., Ltd., was employed as the measuring apparatus and afour-point probe, MCP-TPO3P manufactured by DIA Instruments Co., Ltd.,was employed as the probe.

(2) White Reflectance

Using “LUMIRROR” ES6R manufactured by Toray Industries, Inc. as a whitereflection plate and “LUCIACS” CS9621T manufactured by Nitto DenkoCorporation as an adhesive layer, they were laminated such that, asshown in FIG. 2, the conductive surface of the transparent conductivelaminate was in contact with the adhesive layer. On the transparentconductive laminate side of the thus obtained laminate, the reflectanceat a wavelength of 550 nm was measured using “CM-2500d” manufactured byKonica Minolta Sensing, Inc., and the thus obtained value was defined aswhite reflectance.

(3) Light Absorptivity of Carbon Nanotube Layer (3-1) Reflectance ofConductive Surface and Reflectance of the Opposite Surface of ConductiveSurface

The opposite surface of the measuring surface was roughened uniformlyusing a #320 to #400 waterproof sandpaper such that the 60°-gloss value(JIS Z 8741 (1997)) became not greater than 10. Then, the thus roughenedsurface was colored by applying thereto a black paint such that thevisible light transmittance became 5% or less. Using a spectrophotometer“UV-3150” manufactured by Shimadzu Corporation, the reflectance of theconductive surface and that of the opposite surface of the conductivesurface were measured at an incidence angle of 5° at the measuringsurface and a wavelength of 550 nm.

(3-2) Light Transmittance

Using a spectrophotometer “UV-3150” manufactured by ShimadzuCorporation, a light was irradiated from the conductive surface side tomeasure the light transmittance at a wavelength of 550 nm.

(3-3) Light Absorptivity of Carbon Nanotube Layer

From the reflectance of the conductive surface, that of the oppositesurface of the conductive surface and the light transmittance that weremeasured in (3-1) and (3-2), the light absorptivity of the carbonnanotube layer was calculated using the following equation.

Light absorptivity of carbon nanotube layer (%)=100%−Light transmittance(%)−Reflectance of conductive surface (%)−Reflectance of the oppositesurface of conductive surface (%)

(4) Total Light Transmittance

In accordance with JIS K 7361 (1997), the total light transmittance wasmeasured using a turbidimeter NDH2000 manufactured by Nippon DenshokuIndustries Co., Ltd.

(5) Water Contact Angle

In an atmosphere having a room temperature of 25° C. and a relativehumidity of 50%, 1 to 4 μL of water was dropped onto the film surfaceusing a syringe. Using a contact angle meter (model CA-X manufactured byKyowa Interface Science Co., Ltd.), a droplet was observed from ahorizontal cross-section to determine the angle created between atangent line of the droplet edge and the film plane.

(6) Heat Resistance Stability

A transparent conductive laminate was sampled in a size of 5 cm×10 cmand subjected to the following heat treatment. The surface resistance ofthe sample after the heat treatment was divided by the surfaceresistance of the sample prior to the heat treatment and the thusobtained value was used as an index of the heat resistance stability.

Heat treatment: the following steps (i) and (ii) were carried outconsecutively.

(i) retaining the sample for 1 hour in a 150° C. hot-air oven; and

(ii) leaving the resulting sample to stand for 24 hours in an atmospherehaving a room temperature of 25° C. and a relative humidity of 50%

(7) Moist-heat Resistance Stability

A transparent conductive laminate was sampled in a size of 5 cm×10 cmand subjected to the following moist-heat treatment. The surfaceresistance of the sample after the moist-heat treatment was divided bythe surface resistance of the sample prior the moist-heat treatment andthe thus obtained value was used as an index of the moist-heatresistance stability.

Moist-heat treatment: the following steps (iii) and (iv) were carriedout consecutively.

(iii) retaining the sample for 1 hour in a moist-heat oven having atemperature of 60° C. and a relative humidity of 90%; and

(iv) leaving the resulting sample for 3 minutes to stand in anatmosphere having a room temperature of 25° C. and a relative humidityof 50%

(8) Long-Term Heat Resistance Stability

A transparent conductive laminate was sampled in a size of 5 cm×10 cmand subjected to the following long-term heat treatment. The surfaceresistance of the sample after the long-term heat treatment was dividedby the surface resistance of the sample prior the long-term heattreatment and the thus obtained value was used as an index of thelong-term heat resistance stability.

Long-term heat treatment: the following steps (v) and (vi) were carriedout consecutively.

(v) retaining the sample for 500 hour in a 80° C. hot-air oven; and

(vi) leaving the resulting sample to stand for 3 minutes in anatmosphere having a room temperature of 25° C. and a relative humidityof 50%

(9) Surface Resistance of Carbon Nanotube Layer at 96% Total LightTransmittance

In accordance with the method described in the section of [Formation ofCarbon Nanotube Layer] below, samples in which the ratio of the totallight transmittance of transparent conductive laminate before and aftercoating a carbon nanotube thereon (total light transmittance of thecarbon nanotube layer) is not less than 96% and samples in which thisratio is not higher than 96% were each prepared in at least one level.For each of the thus prepared samples, the surface resistance and thetotal light transmittance of the carbon nanotube layer were measured tocalculate the surface resistance of the carbon nanotube layer at 96%total light transmittance by interpolation.

(10) Surface Resistance at 75% White Reflectance

In accordance with the method described in the section of [Formation ofCarbon Nanotube Layer] below, samples in which the white reflectanceafter the formation of an overcoat layer is not less than 75% andsamples in which this white reflectance is not higher than 75% were eachprepared in at least one level. For each of the thus prepared samples,the surface resistance and the white reflectance were measured tocalculate the surface resistance at 75% white reflectance byinterpolation.

(11) Surface Resistance of Carbon Nanotube Layer at 5% LightAbsorptivity

In accordance with the method described in the section of [Formation ofCarbon Nanotube Layer] below, samples in which the light absorptivity ofthe carbon nanotube layer after the formation of an overcoat layer isnot less than 5% and samples in which this light absorptivity of thecarbon nanotube layer is not higher than 5% were each prepared in atleast one level. For each of the thus prepared samples, the surfaceresistance and the light absorptivity of the carbon nanotube layer weremeasured to calculate the surface resistance of the carbon nanotubelayer at 5% light absorptivity of by interpolation.

(12) Surface Resistance of Carbon Nanotube Layer at 90% Total LightTransmittance after Formation of Overcoat Layer

In accordance with the method described in the section of [Formation ofCarbon Nanotube Layer] below, samples in which the total lighttransmittance after the formation of an overcoat layer is not less than90% and samples in which this total light transmittance is not higherthan 90% were each prepared in at least one level. For each of the thusprepared samples, the surface resistance and the total lighttransmittance of the carbon nanotube layer were measured to calculatethe surface resistance of Carbon Nanotube Layer at 90% total lighttransmittance by interpolation.

(13) Thickness of Undercoat Layer

With only an undercoat layer being provided on a PET film used as asubstrate, the opposite surface of the surface provided with theundercoat layer was roughened uniformly using a #320 to #400 waterproofsandpaper such that the 60°-gloss value (JIS Z 8741 (1997)) became notgreater than 10. Then, the thus roughened surface was colored byapplying thereto a black paint such that the visible light transmittancebecame 5% or less. Using a spectrophotometer (UV-3150) manufactured byShimadzu Corporation, at an incidence angle of 5° at the measuringsurface, the absolute reflectance spectrum in a wavelength region of 200nm to 1,200 nm was measured at 1-nm intervals to determine thewavelength showing the minimum reflectance in a region of 200 nm to1,200 nm.

d _(U)=λ/4n

(d_(U): thickness of undercoat layer (nm), λ: wavelength showing theminimum reflectance (nm), n: refractive index of transparent protectivefilm (material: silica), 1.44)

It is noted here that, in the present examples, in cases where λ wassmaller than 200 nm or larger than 1,200 nm, a theoretical thickness ofthe undercoat layer, which is described below, was used instead as thethickness of the undercoat layer.

Theoretical thickness (nm)=(Solids concentration of coating solution (wt%)/100)×Wire bar number (μm)×1.5×1/1,000

(14) Thickness of Overcoat Layer

With only an overcoat layer being provided on a PET film which used as asubstrate, the opposite surface of the surface provided with theovercoat layer was roughened uniformly using a #320 to #400 waterproofsandpaper such that the 60°-gloss value (JIS Z 8741 (1997)) became notgreater than 10. Then, the thus roughened surface was colored byapplying thereto a black paint such that the visible light transmittancebecame 5% or less. Using a spectrophotometer (UV-3150) manufactured byShimadzu Corporation, at an incidence angle of 5° at the measuringsurface, the absolute reflectance spectrum in a wavelength region of 200nm to 1,200 nm was measured at 1-nm intervals to determine thewavelength showing the minimum reflectance in a region of 200 nm to1,200 nm.

d _(O)=λ/4n

(d_(O): thickness of overcoat layer (nm), λ: wavelength showing theminimum reflectance (nm), n: refractive index of transparent protectivefilm (material: silica), 1.44)

It is noted here that, also for the thickness of the overcoat layer, incases where λ was smaller than 200 nm or larger than 1,200 nm, atheoretical thickness derived in the same manner as that of theundercoat layer was used instead as the thickness of the overcoat layer.

(15) XPS

Using “Quantera SXM” manufactured by Ulvac-Phi, Inc., the C_(I), bindingenergy was measured with AlK_(α1,2) excitation X-ray (1486.6 eV) at aphotoelectron X-ray angle of 15°. In this case, abscissa correction wasperformed to a C_(1s) main peak of 284.6 eV.

(16) Wettability of Carbon Nanotube Dispersion Liquid with Surface ofUndercoat Layer or PET Substrate

As for the wettability of a carbon nanotube dispersion liquid with asurface of undercoat layer or a surface of PET substrate, the carbonnanotube dispersion liquid was applied and dry-fixed onto theabove-described surface of undercoat layer or the surface of PETsubstrate and the resulting dry carbon nanotube coating film wasvisually observed. When the coating film was uniformly formed, thewettability was judged as satisfactory, and when the coating film wasnot uniformly formed, the wettability was judged as poor.

[Undercoat Layer Formation Example 1]

By the following operations, a hydrophilic silica undercoat layercontaining silica microparticles of about 30 nm in diameter exposed onthe surface was formed using polysilicate as a binder.

A Mega Aqua Hydrophilic DM Coat (DM-30-26G-N1; manufactured by RyowaCorporation) containing hydrophilic silica microparticles of about 30 nmin diameter and polysilicate was used as a coating solution for silicafilm formation.

Using a #8 wire bar, the above-described coating solution for silicafilm formation was applied onto a 188 μm-thick biaxially-stretchedpolyethylene terephthalate film, “LUMIRROR” U46 manufactured by TorayIndustries, Inc. Then, the resultant was dried for 1 minute in a dryerat 80° C.

FIG. 3 shows a surface AFM image.

[Undercoat Layer Formation Example 2]

A hydrophilic silica undercoat layer containing silica microparticles ofabout 30 nm in diameter exposed on the surface was formed usingpolysilicate as a binder in the same manner as in [Undercoat LayerFormation Example 1] except that a #3 wire bar was used.

[Undercoat Layer Formation Example 3]

A hydrophilic silica undercoat layer containing silica microparticles ofabout 30 nm in diameter exposed on the surface was formed usingpolysilicate as a binder in the same manner as in [Undercoat LayerFormation Example 1] except that a Mega Aqua Hydrophilic DM CoatDM-30-26G-N-1-A (manufactured by Ryowa Corporation; having a slightlylower hydrophilicity as compared to the one used in [Undercoat LayerFormation Example 1]) containing hydrophilic silica microparticles ofabout 30 nm in diameter and polysilicate was used as the coatingsolution for silica film formation.

[Undercoat Layer Formation Example 4]

By the following operations, a hydrophilic silica undercoat layercomposed of a silica prepared by a sol-gel method was formed.

In a 100-mL plastic container, 20 g of ethanol was placed and 40 g ofn-butyl silicate was added thereto and stirred for 30 minutes. Then,after adding thereto 10 g of 0.1N hydrochloric acid aqueous solution,the resultant was stirred for 2 hours and left to stand at 4° C. for 12hours. The resulting solution was diluted with a mixed solution oftoluene, isopropyl alcohol and methyl ethyl ketone to a solidsconcentration of 1.0% by mass, thereby obtaining a coating solution.

The thus obtained coating solution was applied onto a LUMIRROR U46manufactured by Toray Industries, Inc. using a #8 wire bar. Then, theresultant was dried for 1 minute in a dryer at 125° C.

Thereafter, a corona treatment was performed by the method shown inFIG. 1. Using a Type-H pinhole tester manufactured by Densok PrecisionIndustry Corp. as a high-voltage application device 101, a DC voltage of10 kV was generated between ground (not shown) and an electrode 102.Then, after separating the electrode 102 and a transparent substrate 104by a distance of 150 μm, a partition wall was arranged therebetween. Anoperation of moving the electrode at a speed of about 2 cm/sec in thedirection of the arrow indicated as “A” in FIG. 1 was performed threetimes.

[Undercoat Layer Formation Example 5]

By the following operations, a hydrophilic alumina undercoat layercomposed of alumina was formed.

Using a roll-up type vacuum vapor deposition apparatus having thestructure shown in FIG. 4, on one side of a 12-μm biaxially-stretchedpolyethylene terephthalate film (“LUMIRROR” 12T705 manufactured by TorayIndustries, Inc.; hereinafter, referred to as polymer film) used as atransparent substrate, an alumina layer was formed by vaporizingaluminum, which was used as a vapor deposition material, by a resistanceheating method and then introducing thereto an oxygen gas. First, in arolling chamber 404 of the roll-up type vapor deposition apparatus 403,a polymer film 401 set on a roll-out roller 405 was unrolled at atransfer rate of 100 m/min and passed through a cooling drum 410 viaguide rolls 407, 408 and 409. From a boat 406 on which a wire ofaluminum or the like was introduced, aluminum was vaporized, and oxygenplasma was irradiated from a plasma electrode 412 having a gasintroduction mechanism at an oxygen gas flow rate of 0.6 L/min and aplasma introducing power of 3.0 kW, thereby forming an aluminum oxidelayer (not shown) on the surface of the polymer film 401 on the coolingdrum 410. Thereafter, the resulting polymer film on which an aluminalayer was formed was rolled up by a roll-up roller 416 via guide rolls413, 414 and 415.

[Undercoat Layer Formation Example 6]

A hydrophilic silica undercoat layer composed of a silica prepared by asol-gel method was formed in the same manner as in [Undercoat LayerFormation Example 4] except that the corona treatment was not performed.

[Substrate Surface Treatment Example 1]

The same corona treatment as in [Undercoat Layer Formation Example 4]was performed on “LUMIRROR” U46 manufactured by Toray Industries, Inc.By this treatment, the hydrophilicity of the substrate surface wasimproved and the water contact angle was reduced from 62° to 52°.

[Catalyst Preparation Example: Catalyst Metal Salt Supported onMagnesia]

Ferric ammonium citrate (2.46 g; manufactured by Wako Pure ChemicalsIndustries, Ltd.) was dissolved in 500 mL of methanol (manufactured byKanto Chemical Co., Inc.). To the resulting solution, 100.0 g ofmagnesium oxide (MJ-30 manufactured by Iwatani Chemical Industry Co.,Ltd.) was added and vigorously stirred for 60 minutes using a stirrer.The resulting suspension was concentrated to dryness under reducedpressure at 40° C. The thus obtained powder was heat-dried at 120° C. toremove methanol, thereby obtaining a catalyst in which a metal salt wassupported on magnesium oxide powder. The thus obtained solid content waspulverized using a mortar and sieved to recover particles having aparticle size in the range of 20 to 32-mesh (0.5 to 0.85 mm). The thusobtained catalyst had an iron content of 0.38% by mass and a bulkdensity of 0.61 g/mL. The above-described operations were repeated andthe resultants were subjected to the following experiments.

[Carbon Nanotube Assembly Production Example: Synthesis of CarbonNanotube Assembly]

Using the apparatus shown in FIG. 5, a carbon nanotube was synthesized.A reactor 503 is a cylindrical quartz tube of 75 mm in inner diameterand 1,100 mm in length. The reactor is equipped with a quartz sinteredplate 502 in the central part; a mixed gas introduction pipe 508, whichis an inert gas and material gas supply line, in the lower part of thequartz tube; and a waste gas pipe 506 in the upper part. Further, thereactor is also equipped with three electric furnace 501 s as heaterssurrounding the periphery thereof such that the reactor can bemaintained at an arbitrary temperature. The reactor is equipped with athermocouple 505 as well for detecting the temperature inside thereactor tube.

A catalyst layer 504 was formed by introducing 132 g of the solidcatalyst prepared in Catalyst Preparation Example onto the quartzsintered plate provided in the central part of the reactor arranged inthe vertical direction. While heating the thus formed catalyst layer,using a mass flow controller 507, a nitrogen gas was fed at a rate of16.5 L/min from the bottom part of the reactor toward the upper partthereof and allowed to pass through the catalyst layer until thetemperature inside the reactor tube became about 860° C. Thereafter,while feeding a nitrogen gas, using the mass flow controller 507, amethane gas was further introduced at a rate of 0.78 L/min for 60minutes and allowed to pass through the catalyst layer, therebyperforming a reaction. Here, the contact time (W/F), which is obtainedby dividing the weight of the solid catalyst with the flow rate ofmethane, was 169 min·g/L and the linear velocity of themethane-containing gas was 6.55 cm/sec. The feeding of methane gas wasterminated and the quartz reactor tube was cooled to room temperaturewhile passing nitrogen gas therethrough at a rate of 16.5 L/min.

Heating was terminated and the reactor was left to cool to roomtemperature. Then, once the reactor was cooled to room temperature, theresulting carbon nanotube-containing composition containing the catalystand carbon nanotube was taken out therefrom.

[Purification and Oxidation Treatment of Carbon Nanotube Assembly]

In 2,000 mL of 4.8N hydrochloric acid aqueous solution, 130 g of thecarbon nanotube-containing composition containing the catalyst andcarbon nanotube, which was obtained in Carbon Nanotube AssemblyProduction Example, was stirred for 1 hour to dissolve iron which is thecatalyst metal and MgO which is the carrier thereof. After filtering theresulting black suspension, the thus obtained filtration product wasagain placed in 400 mL of 4.8N hydrochloric acid aqueous solution toperform a MgO removal treatment and the resultant was filtered. Theseoperations were repeated three times (MgO removal treatment). Then,after washing the resultant with ion-exchanged water until thesuspension of filtration product became neutral, the resulting carbonnanotube-containing composition was stored in wet condition with water.Here, the total weight of the carbon nanotube-containing composition inwet condition with water was 102.7 g (concentration of carbonnanotube-containing composition: 3.12% by mass).

To the thus obtained carbon nanotube-containing composition in wetcondition, a concentrated nitric acid (manufactured by Wako PureChemicals Industries, Ltd.; first class, assay 60 to 61%) was added in aweight of about 300 times of the dry weight of the carbonnanotube-containing composition. Then, in an oil bath at about 140° C.,the resulting mixture was heated to reflux with stirring for 25 hours.Thereafter, the resulting nitric acid solution containing the carbonnanotube-containing composition was 3-fold diluted with ion-exchangedwater and suction-filtered. After washing the resultant withion-exchanged water until the suspension of filtration product becameneutral, a carbon nanotube assembly was obtained in wet condition withwater. Here, the total weight of the carbon nanotube-containingcomposition in wet condition with water was 3.351 g (concentration ofcarbon nanotube-containing composition: 5.29 wt %).

[Preparation of Carbon Nanotube Dispersion Liquid 1]

The thus obtained carbon nanotube assembly in wet condition (25 mg basedon dry weight), 2.5 g of 1% by mass sodium carboxymethyl celluloseaqueous solution (DAICEL 1140 manufactured by Daicel FineChem. Ltd.(weight average molecular weight: 450,000)) and 6.7 g of zirconia beads(TORAYCERAM manufactured by Toray Industries, Inc.; beads size: 0.8 mm)were added to a container and the resulting mixture was adjusted to havea pH of 10 using 28% aqueous ammonia solution (manufactured by KishidaChemical Co., Ltd.). This container was shaken for 2 hours using avibration ball mill (VS-1 manufactured by Irie Shokai Co., Ltd.;vibration rate: 1,800 cpm (60 Hz)) to prepare a carbon nanotube paste.

Then, the thus obtained carbon nanotube paste was diluted withion-exchanged water to a carbon nanotube concentration of 0.15% by massand 10 g of the resulting diluent was again adjusted to have a pH of 10using 28% aqueous ammonia solution. The thus obtained aqueous solutionwas subjected to a 1.5-minute dispersion treatment with ice cooling,using an ultrasonic homogenizer (VCX-130 manufactured by leda TradingCorporation) at an output of 20 W (1 kW·min/g). During this dispersiontreatment, the solution temperature was maintained at not higher than10° C. The resulting solution was centrifuged at 10,000 G for 15 minutesusing a high-speed centrifuge (MX-300 manufactured by Tomy Seiko Co.,Ltd.) to obtain a carbon nanotube dispersion liquid in an amount of 9 g.

[Preparation of Carbon Nanotube Dispersion Liquid 2]

The thus obtained carbon nanotube assembly in wet condition (25 mg basedon dry weight), 0.833 g of 6% by mass sodium carboxymethyl celluloseaqueous solution (CELLOGEN 5A manufactured by Dai-Ichi Kogyo SeiyakuCo., Ltd. (weight average molecular weight: 80,000)), 0.8 g ofion-exchanged water and 13.3 g of zirconia beads (TORAYCERAMmanufactured by Toray Industries, Inc.; beads size: 0.8 mm) were addedto a container and the resulting mixture was adjusted to have a pH of 10using 28% aqueous ammonia solution (manufactured by Kishida ChemicalCo., Ltd.) (dispersant/carbon nanotube mass ratio=2). This container wasshaken for 2 hours using a vibration ball mill (VS-1 manufactured byIrie Shokai Co., Ltd.; vibration rate: 1,800 cpm (60 Hz)) to prepare acarbon nanotube paste.

Then, the thus obtained carbon nanotube paste was diluted withion-exchanged water to a carbon nanotube concentration of 0.15% by massand 10 g of the resulting diluent was again adjusted to have a pH of 10using 28% aqueous ammonia solution. The thus obtained aqueous solutionwas subjected to a 1.5-minute dispersion treatment with ice cooling,using an ultrasonic homogenizer (VCX-130 manufactured by Ieda TradingCorporation) at an output of 20 W (0.6 kW·min/g). During this dispersiontreatment, the solution temperature was maintained at not higher than10° C. The resulting solution was centrifuged at 10,000 G for 15 minutesusing a high-speed centrifuge (MX-300 manufactured by Tomy Seiko Co.,Ltd.) to obtain a carbon nanotube dispersion liquid in an amount of 9 g.Thereafter, water was added thereto to a final carbon nanotube assemblyconcentration of 0.08% by mass to prepare a film coating solution.

[Preparation of Carbon Nanotube Dispersion Liquid 3]

A carbon nanotube dispersion liquid was obtained in an amount of 9 g inthe same manner as in the preparation of the carbon nanotube dispersionliquid 2 except that the amount of 6% by mass sodium carboxymethylcellulose was changed to 1.04 g (dispersant/carbon nanotube massratio=2.5).

[Preparation of Carbon Nanotube Dispersion Liquid 4]

A carbon nanotube dispersion liquid was obtained in an amount of 9 g inthe same manner as in the preparation of the carbon nanotube dispersionliquid 2 except that the amount of 6% by mass sodium carboxymethylcellulose was changed to 1.25 g (dispersant/carbon nanotube massratio=3).

[Preparation of Carbon Nanotube Dispersion Liquid 5]

A carbon nanotube dispersion liquid was obtained in an amount of 9 g inthe same manner as in the preparation of the carbon nanotube dispersionliquid 2 except that the amount of 6% by mass sodium carboxymethylcellulose was changed to 2.50 g (dispersant/carbon nanotube massratio=6).

[Preparation of Carbon Nanotube Dispersion Liquid 6]

In a 20-mL container, 15 mg (based on dry mass) of the carbon nanotubeobtained in the above carbon nanotube-containing composition productionstep and 300 mg of a 30% by mass ammonium polystyrene sulfonate aqueoussolution (manufactured by Aldrich; weight average molecular weight:200,000) (dispersant/carbon nanotube mass ratio=6) were weighed anddistilled water was added thereto to a total weight of 10 g. Theresulting solution was subjected to a 7.5-minute dispersion treatmentwith ice cooling using an ultrasonic homogenizer (VCX-130 manufacturedby Ieda Trading Corporation) at an output of 20 W, thereby preparing acarbon nanotube solution. In this solution, the mass ratio of thedispersant with respect to the mass of carbon nanotube is 6. The thusobtained solution was centrifuged at 10,000 G for 15 minutes using ahigh-speed centrifuge (MX-300 manufactured by Tomy Seiko Co., Ltd.) toobtain a carbon nanotube dispersion liquid in an amount of 9 g.

[Preparation of Carbon Nanotube Dispersion Liquid 7]

A carbon nanotube dispersion liquid was obtained in an amount of 9 g inthe same manner as in the preparation of the carbon nanotube dispersionliquid 2 except that the pH at the time of adjusting the carbon nanotubepaste and the carbon nanotube dispersion liquid was changed to 4.5.

[Preparation of Carbon Nanotube Dispersion Liquid 8]

A carbon nanotube dispersion liquid was obtained in an amount of 9 g inthe same manner as in the preparation of the carbon nanotube dispersionliquid 2 except that the pH at the time of adjusting the carbon nanotubepaste and the carbon nanotube dispersion liquid was changed to 5.5.

[Preparation of Carbon Nanotube Dispersion Liquid 9]

A carbon nanotube dispersion liquid was obtained in an amount of 9 g inthe same manner as in the preparation of the carbon nanotube dispersionliquid 2 except that the pH at the time of adjusting the carbon nanotubepaste and the carbon nanotube dispersion liquid was changed to 7.

[Preparation of Carbon Nanotube Dispersion Liquid 10]

A carbon nanotube dispersion liquid was obtained in an amount of 9 g inthe same manner as in the preparation of the carbon nanotube dispersionliquid 2 except that the pH at the time of adjusting the carbon nanotubepaste and the carbon nanotube dispersion liquid was changed to 9.

[Preparation of Carbon Nanotube Dispersion Liquid 11]

A carbon nanotube dispersion liquid was obtained in an amount of 9 g inthe same manner as in the preparation of the carbon nanotube dispersionliquid 2 except that the pH at the time of adjusting the carbon nanotubepaste and the carbon nanotube dispersion liquid was changed to 11.

[Preparation of Carbon Nanotube Dispersion Liquid 12]

The thus obtained carbon nanotube assembly in wet condition (15 mg basedon dry weight) and 4.5 g of 1 wt % sodium carboxymethyl celluloseaqueous solution (manufactured by Sigma, 90 kDa, 50 to 200 cps)(dispersant/carbon nanotube mass ratio=3) were weighed and ion-exchangedwater was added thereto to a total weight of 10 g. The resultingsolution was adjusted to have a pH of 4.0 using nitric acid and thensubjected to a 7.5-minute dispersion treatment with ice cooling using anultrasonic homogenizer (CX-130 manufactured by Ieda Trading Corporation)at an output of 20 W, thereby preparing a carbon nanotube solution.During this dispersion treatment, the solution temperature wasmaintained at not higher than 10° C. The resulting solution wascentrifuged at 10,000 G for 15 minutes using a high-speed centrifuge(MX-300 manufactured by Tomy Seiko Co., Ltd.) to obtain a carbonnanotube dispersion liquid in an amount of 9 g.

[Formation of Carbon Nanotube Layer]

Ion-exchanged water was added to the above-described carbon nanotubedispersion liquid to adjust the amount of carbon nanotube to 0.03% bymass to 0.04% by mass. Then, the resulting carbon nanotube dispersionliquid was, using a wire bar, applied onto a transparent substrate orPET transparent substrate on which the above-described undercoat wasformed, and the resultant was dried for 1 minute in a dryer at 80° C. tofix the carbon nanotube composition. The light transmittance wasadjusted by adjusting the above-described carbon nanotube concentrationand wire bar number.

[Rinse Treatment]

The transparent conductive laminate on which a carbon nanotube layer wasthus formed was rinsed with ion-exchanged water for 30 seconds to removethe dispersant. Thereafter, water droplets adhering to the film wereremoved using an air duster and the resultant was then dried at normaltemperature.

[Overcoat Layer Formation Example 1]

In a 100-mL plastic container, 20 g of ethanol was placed and 40 g ofn-butyl silicate was added thereto and stirred for 30 minutes. Then,after adding thereto 10 g of 0.1N hydrochloric acid aqueous solution,the resultant was stirred for 2 hours and left to stand at 4° C. for 12hours. The resulting solution was diluted with a mixed solution oftoluene, isopropyl alcohol and methyl ethyl ketone to a solidsconcentration of 0.1% by mass.

The thus obtained coating solution was applied onto a carbon nanotubelayer using a #8 wire bar. Then, the resultant was dried for 1 minute ina dryer at 125° C.

[Overcoat Layer Formation Example 2]

An overcoat layer was formed in the same manner as in [Overcoat LayerFormation Example 1] except that the dilution with the mixed solution oftoluene, isopropyl alcohol and methyl ethyl ketone was performed to asolids concentration of 1% by mass.

Example 1

An undercoat layer was formed in accordance with [Undercoat LayerFormation Example 1]. Further, on this undercoat layer, a carbonnanotube layer was formed using the carbon nanotube dispersion liquid 1.Then, on this carbon nanotube layer, an overcoat layer was formed by themethod of [Overcoat Layer Formation Example 1] to prepare a transparentconductive laminate.

Examples 2 to 13 and Comparative Examples 1 to 6

The respective transparent conductive laminates were prepared in thesame manner as in Example 1 except that the combination of the substratesurface treatment, undercoat layer formation, carbon nanotube dispersionliquid, overcoat layer formation and rinse treatment was changed asshown in Table 1. It is noted here that, in Table 1, the indication“None” for the item “Substrate surface treatment or undercoat layer”denotes that the carbon nanotube dispersion liquid was directly appliedwithout forming an undercoat on the “LUMIRROR” U46 manufactured by TorayIndustries, Inc. or without subjecting the substrate to a coronatreatment.

TABLE 1 Substrate Surface Treatment or Carbon Nanotube Rinse UndercoatLayer Formation Dispersion Liquid treatment Overcoat Layer Example 1Undercoat Layer Formation Carbon Nanotube absence Overcoat LayerFormation Example 1 Dispersion Liquid 1 Example 1 Example 2 UndercoatLayer Formation Carbon Nanotube absence Overcoat Layer Formation Example1 Dispersion Liquid 2 Example 1 Example 3 Undercoat Layer FormationCarbon Nanotube absence Overcoat Layer Formation Example 1 DispersionLiquid 4 Example 1 Example 4 Undercoat Layer Formation Carbon Nanotubeabsence Overcoat Layer Formation Example 1 Dispersion Liquid 5 Example 1Example 5 Undercoat Layer Formation Carbon Nanotube absence OvercoatLayer Formation Example 3 Dispersion Liquid 2 Example 1 Example 6Undercoat Layer Formation Carbon Nanotube absence Overcoat LayerFormation Example 4 Dispersion Liquid 1 Example 2 Example 7 UndercoatLayer Formation Carbon Nanotube absence Overcoat Layer Formation Example5 Dispersion Liquid 1 Example 2 Example 8 Undercoat Layer FormationCarbon Nanotube absence Overcoat Layer Formation Example 1 DispersionLiquid 6 Example 1 Example 9 Undercoat Layer Formation Carbon Nanotubeabsence Overcoat Layer Formation Example 1 Dispersion Liquid 8 Example 1Example 10 Undercoat Layer Formation Carbon Nanotube absence OvercoatLayer Formation Example 1 Dispersion Liquid 9 Example 1 Example 11Undercoat Layer Formation Carbon Nanotube absence Overcoat LayerFormation Example 1 Dispersion Liquid 10 Example 1 Example 12 UndercoatLayer Formation Carbon Nanotube absence Overcoat Layer Formation Example1 Dispersion Liquid 11 Example 1 Example 13 Undercoat Layer FormationCarbon Nanotube absence Overcoat Layer Formation Example 2 DispersionLiquid 3 Example 2 Comparative Substrate Surface Treatment CarbonNanotube absence Overcoat Layer Formation Example 1 Example 1 DispersionLiquid 1 Example 1 Comparative Substrate Surface Treatment CarbonNanotube absence Overcoat Layer Formation Example 2 Example 11Dispersion Liquid 1 Example 2 Comparative absence Carbon Nanotubeabsence Overcoat Layer Formation Example 3 Dispersion Liquid 6 Example 1Comparative Undercoat Layer Formation Carbon Nanotube absence absenceExample 4 Example 6 Dispersion Liquid 1 Comparative Undercoat LayerFormation Carbon Nanotube absence Overcoat Layer Formation Example 5Example 1 Dispersion Liquid 7 Example 1 Comparative absence CarbonNanotube presence Overcoat Layer Formation Example 6 Dispersion Liquid12 Example 2

Table 2 shows, with regard to Examples 1 to 13 and Comparative Examples1 to 6: the dispersant/carbon nanotube mass ratio; pH of the carbonnanotube dispersion liquid; water contact angle of the surface of theundercoat layer or the PET transparent substrate; thickness of theundercoat layer; wettability of the carbon nanotube dispersion liquidwith the surface of the undercoat layer or the PET transparentsubstrate; surface resistance of the carbon nanotube layer at 96% totallight transmittance; surface resistance at 75% white reflectance;surface resistance of the carbon nanotube layer at 5% lightabsorptivity; thickness of the overcoat layer; surface resistance of thecarbon nanotube layer at 90% total light transmittance after formationof the overcoat layer; heat resistance stability; moist-heat resistancestability; and long-term heat resistance stability. In Table 2, “-”denotes the absence of corresponding item and “N.D.” denotes the absenceof evaluation data.

TABLE 2 Wettability of Carbon Surface Water contact Nanotube Resistanceof angle of the Dispersion Carbon pH of the surface of the Liquid withthe Nanotube Layer Surface Dispersant/ carbon undercoat ThicknessSurface of at 96% Total Resistance at carbon nanotube layer or the ofthe Undercoat Layer Light 75% White nanotube dispersion PET substrateundercoat or PET Transmittance Reflectance mass ratio liquid (°) layer(nm) Substrate (Ω/□) (Ω/□) Example 1 1 10 5.5 100 good 7.0 × 10² 9.0 ×10² Example 2 2 10 5.5 100 good 4.0 × 10² 4.5 × 10² Example 3 3 10 5.5100 good 4.0 × 10² 4.5 × 10² Example 4 6 10 5.5 100 good 4.5 × 10² 5.5 ×10² Example 5 2 10 13 100 good 4.5 × 10² 7.0 × 10² Example 6 1 10 7.1100 good 6.0 × 10² 7.0 × 10² Example 7 1 10 23 100 good 6.0 × 10² 7.2 ×10² Example 8 6 10 5.5 100 good 6.4 × 10² 8.0 × 10² Example 9 2 5.5 5.5100 good 6.2 × 10² 7.5 × 10² Example 10 2 7.0 5.5 100 good 4.6 × 10² 5.4× 10² Example 11 2 9.0 5.5 100 good 4.0 × 10² 4.5 × 10² Example 12 2 115.5 100 good 4.2 × 10² 5.0 × 10² Example 13 2.5 10 5.5  40 good 4.0 ×10² 4.2 × 10² Comparative 1 10 52 — good 1.4 × 10³ 1.6 × 10³ Example 1Comparative 1 10 52 — good 1.5 × 10³ 1.7 × 10³ Example 2 Comparative 610 62 100 good 1.7 × 10³ 1.2 × 10³ Example 3 Comparative 1 10 63 100 bad— — Example 4 Comparative 2 4.5 5.5 100 good 1.3 × 10³ 1.4 × 10³ Example5 Comparative 1 4.0 62 — good 4.0 × 10² 4.6 × 10² Example 6 SurfaceSurface Resistance of Resistance of Carbon Nanotube Carbon Layer at 90%Nanotube Thickness Total Light Layer at 5% of the Transmittance Moist-Long-term Light overcoat after Formation of Heat heat heat Absorptivitylayer Overcoat Layer resistance resistance resistance (Ω/□) (nm) (Ω/□)stability stability stability Example 1 9.0 × 10² 12 9.0 × 10² 1.0 1.0N.D. Example 2 4.5 × 10² 12 4.5 × 10² 1.0 0.8 1.9 Example 3 4.5 × 10² 124.5 × 10² 1.0 0.9 1.9 Example 4 5.5 × 10² 12 5.5 × 10² 1.0 0.9 N.D.Example 5 7.0 × 10² 12   7 × 10² 1.1 1.0 N.D. Example 6 7.0 × 10² 60 1.5× 10³ 1.0 1.2 N.D. Example 7 7.2 × 10² 60 2.0 × 10³ 0.8 1.2 N.D. Example8 8.0 × 10² 12 8.0 × 10² 1.2 N.D. N.D. Example 9 7.5 × 10² 12 7.5 × 10²1.0 0.9 N.D. Example 10 5.4 × 10² 12 5.4 × 10² 1.2 1.0 N.D. Example 114.5 × 10² 12 4.5 × 10² 1.1 1.0 N.D. Example 12 5.0 × 10² 12 5.0 × 10²1.1 1.0 N.D. Example 13 4.2 × 10² 60 4.2 × 10² 0.8 0.9 1.0 Comparative1.6 × 10³ 12 1.6 × 10³ 1.5 2.0 N.D. Example 1 Comparative 1.7 × 10³ 601.7 × 10³ 0.9 1.5 N.D. Example 2 Comparative 1.2 × 10³ 12 1.2 × 10³ 1.1N.D. N.D. Example 3 Comparative — — — — — N.D. Example 4 Comparative 1.4× 10³ 12 1.4 × 10³ 1.0 0.9 N.D. Example 5 Comparative 4.6 × 10² 80 4.6 ×10² 1.5 1.5 1.0 Example 6

[XPS Measurement Sample 1]

On the substrate on which an undercoat layer was formed in [UndercoatLayer Formation Example 2], a coating solution adjusted to contain 0.06%by mass of the [carbon nanotube dispersion liquid 3] was coated using a#3 wire bar.

[XPS Measurement Sample 2]

A #188 U46 on which no undercoat layer was formed was subjected to thecorona treatment performed in [Undercoat Layer Formation Example 4].Further, on the resultant, a coating solution adjusted to contain 0.06%by mass of the [carbon nanotube dispersion liquid 3] was coated using a#20 wire bar. Here, the reason why the thickness of the carbon nanotubelayer was increased by using a #20 wire bar as compared to the XPSMeasurement Sample 1 was to prevent X-ray from penetrating into the PETsubstrate. By doing so, only the information relevant to the bindingstate of carbon in the carbon nanotube layer can be obtained.

The surfaces of the [XPS Measurement Sample 1] and the [XPS MeasurementSample 2] were analyzed by XPS. The results thereof are shown in FIG. 6.From FIG. 6, it was found that the carbon bond peaks, which areattributed to carboxymethylcellulose in the outermost surface (see FIG.7 for the binding state of carbon for each of “a”, “b” and “c), werehigher for the [XPS Measurement Sample 2] as compared to the [XPSMeasurement Sample 1]; and that, by providing an undercoat layer, therewas a relative decrease in the amount of carboxymethylcellulose in thecarbon nanotube layer.

In order to compare the amounts of carboxymethylcellulose morequantitatively, element composition ratios were derived from XPS data.The results thereof are shown in Table 3. Elemental silicon was observedin the XPS Measurement Sample 1 in which an undercoat layer wasprovided; however, in the XPS Measurement Sample 2 in which no undercoatlayer was provided, elemental silicon was not observed. The XPSMeasurement Sample 1 contains oxygen attributed to silicon oxide (SiO₂)in the undercoat layer. Table 4 shows the results obtained bysubtracting this oxygen content, which are the elemental analysisresults relating only to the respective carbon nanotube layers. It isbelieved that all of oxygen in Table 4 is contained incarboxymethylcellulose of the carbon nanotube layers; therefore, basedon the amounts thereof, the amounts of carboxymethylcellulose in thecarbon nanotube layers can be compared. From Table 5, it was found thatthe [XPS Measurement Sample 2] had a higher oxygen ratio and thus agreater amount of carboxymethylcellulose with respect to the carbonnanotube, as compared to the [XPS Measurement Sample 1].

TABLE 3 Elemental ratio (atomic %) C N O Na Si XPS measuring sample 172.6 — 23.1 1.2 3.1 XPS measuring sample 2 70.2 0.8 26.5 2.5 —

TABLE 4 Elemental ratio (atomic %) C N O Na XPS measuring sample 1 79.9— 18.7 1.3 XPS measuring sample 2 70.2 0.8 26.5 2.5

The transparent conductive laminate according to the present inventionwhich has transparent conductivity, heat resistance stability andmoist-heat resistance stability can be preferably used, for example, asan electrode related to displays such as touch screens, liquid crystaldisplays, organic electroluminescences and electric papers.

DESCRIPTION OF SYMBOLS

-   -   101: High-voltage application device    -   102: Electrode    -   103: Partition wall    -   104: Transparent substrate    -   201: White reflection plate    -   202: Adhesive layer    -   203: Transparent conductive laminate    -   204: Conductive layer    -   205: Transparent substrate    -   401: Polymer film    -   403: Roll-up type vapor deposition apparatus    -   404: Rolling chamber    -   405: Roll-out roller    -   406: Boat    -   407, 408, 409: Roll-out side guide roll    -   410: Cooling drum    -   411: Oxygen introduction nozzle    -   412: Plasma electrode    -   413, 414, 415: Roll-up side guide roll    -   416: Roll-up roller    -   501: Electric furnace    -   502: Quartz sintered plate    -   503: Reactor    -   504: Catalyst layer    -   505: Thermocouple    -   506: Waste gas pipe    -   507: Mass flow controller    -   508: Mixed gas introduction pipe

1. A transparent conductive laminate, which comprises a conductive layercontaining a carbon nanotube on a transparent substrate, wherein atleast one of the following conditions [A] to [C] is satisfied and theratio of the surface resistance after subjecting said transparentconductive laminate to a 1-hour moist-heat treatment at a temperature of60° C. and a relative humidity of 90% and then leaving the resultant tostand for 3 minutes at a temperature of 25° C. and a relative humidityof 50% is 0.7 to 1.3 with respect to the surface resistance prior tosaid treatment: [A] the surface resistance at a white reflectance of 75%is 1.1×10³Ω/□ or less; [B] the surface resistance at a lightabsorptivity of a carbon nanotube layer of 5% is 1.1×10³ Ω/□ or less;and [C] the surface resistance at a total light transmittance of 90% is1.1×10³ Ω/□ or less.
 2. The transparent conductive laminate according toclaim 1, wherein the ratio of the surface resistance after subjectingsaid transparent conductive laminate to a 1-hour heat treatment at atemperature of 150° C. and then leaving the resultant to stand for 24hours at a temperature of 25° C. and a relative humidity of 50% is 0.7to 1.3 with respect to the surface resistance prior to said treatment.3. The transparent conductive laminate according to claim 1, wherein theratio of the surface resistance after subjecting said transparentconductive laminate to a 500-hour heat treatment at a temperature of 80°C. and then leaving the resultant to stand for 3 minutes at atemperature of 25° C. and a relative humidity of 50% is 0.7 to 1.3 withrespect to the surface resistance prior to said treatment.
 4. Thetransparent conductive laminate according to claim 1, wherein anundercoat layer containing an inorganic oxide is arranged underneathsaid conductive layer.
 5. The transparent conductive laminate accordingto claim 4, wherein said inorganic oxide contains alumina and/or silicaas a main component(s).
 6. The transparent conductive laminate accordingto claim 4, wherein said undercoat layer contains a complex of a silicamicroparticle and a polysilicate as a main component.
 7. The transparentconductive laminate according to claim 6, wherein said silicamicroparticle has a diameter in the range of 10 nm to 200 nm.
 8. Amethod of producing a transparent conductive laminate, which comprisesthe steps of: forming an undercoat layer on a transparent substrate,wherein a water contact angle of said undercoat layer is 5 to 25°;coating a carbon nanotube dispersion liquid containing a dispersant onsaid undercoat layer; and drying the resultant to remove a dispersionmedium from said carbon nanotube dispersion liquid coated on saidundercoat layer.
 9. The method of producing a transparent conductivelaminate according to claim 8, wherein said carbon nanotube dispersionliquid has a pH in the range of 5.5 to
 11. 10. The method of producing atransparent conductive laminate according to claim 8, wherein, in saidcoating step and/or drying step, said dispersant is transferred from thecarbon nanotube surface and/or said carbon nanotube dispersion liquid tosaid undercoat layer.
 11. The method of producing a transparentconductive laminate according to claim 8, wherein the mass ratio of saiddispersant is 0.5 to 9 with respect to a carbon nanotube contained insaid carbon nanotube dispersion liquid.
 12. An electric paper,comprising the transparent conductive laminate according to claim
 1. 13.A touch screen, comprising the transparent conductive laminate accordingto claim 1.